INTERACTION BETWEEN GLYCOGEN-PHOSPHORYLASE AND SARCOPLASMIC-RETICULUMMEMBRANES AND ITS FUNCTIONAL IMPLICATIONS

Skeletal muscle glycogen phosphorylase b binds to sarcoplasmic reticul um (SR) membranes with a dissociation constant of 1.7 +/- 0.6 mg of ph osphorylase/ml at 25 degrees C at physiological pH and ionic strength. Raising the temperature to 37 degrees C produced a 2-3-fold decrease in the dissociation constant. The SR membranes could bind up to 1.1 +/ - 0.1 mg of glycogen phosphorylase b/mg of SR protein, whereas liposom es prepared with endogenous SR lipids and reconstituted Ca2+-ATPase we re unable to bind glycogen phosphorylase, Binding of glycogen phosphor ylase b to SR membranes is accompanied by inhibition of its activity i n the presence of AMP. The V-max for glycogen phosphorylase b associat ed with SR membranes is 40 +/- 5% of that for purified glycogen phosph orylase and shows a decreased affinity for its allosteric activators, AMP and IMP. These kinetic effects are also observed with purified gly cogen phosphorylase b when starch or cu-amylose is used as substrate i nstead of glycogen. Treatment of SR membranes with alpha-amylase produ ced dissociation of glycogen phosphorylase b from the SR membranes. Th us, linear polysaccharide fragments of glycogen bound to the SR membra nes are likely mediating the binding of glycogen phosphorylase b to th ese membranes.